STRAIN IN DISTAL TIBIAL OSTEOTOMY STABILISED WITH METAPHYSEAL AND DISTAL TIBIAL LOCKING COMPRESSION PLATES

Abstract

Background: Locking plates are used frequently in distal tibial fractures. We tested two different types of locking compression plates (LCP): the metaphyseal plate (MP) and the distal tibial plate (DTP). We evaluated the strain imposed on an experimental tibial osteotomy, and the stability of plate-tibia (composite bone) construct using LCP-MP and LCP-DTP.

Materials and methods: Twin strain gauged special composite tibial bones were used to simulate the human tibiae. We tested 5 tibiae: one was used as control, two tibiae were tested using LCP-MP, and two with LCP-DTP. Strain was measured by subjecting each construct to a cyclic load of 700 N at 3 Hz in neutral, flexion, extension and torsion to simulate the normal walking cycle.

Results: When compared with the control tibia, strain during the neutral moment at the proximal and distal strain gauge site in the LCP-MP and LCP-DTP constructs decreased by 6.4%/−41.5% and −39%/−47%, respectively. In flexion, the strain increased consistently in both the proximal and distal strain gauge sites using the LCP-MP by 34% and 109%. Using the LCP-DTP, the strain at the proximal strain gauge site decreased by 0.2% and increased by 18% at the distal strain gauge site. In extension, strain decreased by 25% at the proximal strain gauge site, and by 60% at the distal strain gauge site in the LCP –MP construct. In the LCP-DTP construct, the strain decreased by 13% at the proximal strain gauge site, and by 21% at the distal strain gauge site. There were no statistically significant torsional differences between LCP-MP and LCP-DTP group (P=0.121). In this experimental setup, the LCP-DTPs offer greater control of strain than LCP-MPs. They also confer greater resistance to fracture macro-movements, and improved stiffness consistently in neutral, flexion, and torsion than LCP-MPs.

Conclusion: The strain from osteotomised tibiae stabilised with LCP-MPs and LCP-DTPs were close to the strain of the control tibia. Both these locking plates were equally good and conferred greater stiffness in all loading positions.